The University of Hong Kong
Hong Kong

Unlike their inorganic counterparts like silicon, organic semiconductors can operate under conditions such as bending or stretching. Usually a thinner film can bend more easily. In addition to bending, a thinner or smaller device can also offer a faster response time, which is particularly important for a sensor application if immediate information is needed.

Fig. 1 Conceptual image of a CRP sensor in a ventricular catheter implanted in blood vessel (a). Transistor channel current increase against CRP concentration (b).

A University of Hong Kong (HKU) research team led by Dr. Paddy Chan Kwok-leung of the mechanical engineering department, in collaboration with Prof. Gilberto Leung Ka-kit, Tsang Wing-Hing Professor in Clinical Neuroscience, Dr. Anderson Tsang Chun-on of surgery, and Prof. Xu Aimin of the department of pharmacology and pharmacy, have developed a C-reactive protein (CRP) sensor integrated onto a medical catheter for direct CRP sensing (see Figure 1). The sensor’s total thickness is less than 1 mm, which reduces sample and data collection from what is currently a few hours down to 10 minutes or less. This mechanically flexible organic electronic device measures the biological information in real time, sensing the CRP level down to 1 μg/mL. The findings were published in the journal Advanced Science.

Fig. 2 The OFET device before and during 100℃-saturated steam sterilization (a). Normalized mobility and threshold voltage change after 30 minutes saturated steam sterilization (b).

CRP level in blood is an important indicator reflecting the level of the inflammation. It is currently tested by blood analysis, which cannot provide real-time patient information. Developing an ultrathin device that allows for conformal and flexible application is challenging. Ultrathin devices crumple and break easily during the deposition and transfer processes. The deposition of the encapsulation layer to protect the device under extreme operating conditions such as high temperature and moisture is another hurdle.

The team developed a capsule-like CTYOP encapsulation layer that allows the device to withstand high pressure, high temperature, and moisture. By using a CYTOP capsule of only 250 nm, the device withstands boiling water or hot steam for more than 30 minutes without degrading performance (see Figure 2). Sterilization compatibility makes the device an appropriate tool to be used with surgical instruments in an operating room, which requires an aseptic environment.

Fig. 3 Demonstration of the transferable property of the device by transferring it to an aneurysm clip, an artificial heart, and a human hand. Scale bar is 5 mm and 500 μm in enlarged view.

To transfer the sensors onto different devices, the team adapted a hydrophilichydrophobic double layer plastic substrate that can be easily detached from the glass holder once in touch with water. Such floating properties make transferring the sensors onto different substrates or objects a lot simpler and, more importantly, the device shows no performance degradation after transferring among different subjects (see Figure 3).